Anytime a communications system is designed to transmit signals at more than one frequency (i.e. a multiple-transmission system), the designer and/or operator of the system is typically concerned with signal distortion. In some multiple-transmissions systems, a significant amount of signal distortion can be found when only one power amplifier is used to amplify all the transmitted signals. This is due to the fact that power amplifiers typically have the ability to provide distortion-free amplification for only a limited range of frequencies. Thus, if the multiple-transmission system requires the transmission of a signal having a frequency outside the distortion-free range of the power amplifier, the signal may be significantly distorted during transmission.
A solution to this problem is to design the multiple-transmission system to provide a separate power amplifier for each transmission signal. Since each amplifier may provide distortion-free amplification at the frequency of its respective signal, this solution insures that signal distortion is minimized during transmission.
Power amplifiers, however, are typically large and expensive devices that require large amounts of direct current (DC) power, and thus relatively large and expensive DC batteries, to operate. As a result, even though using separate amplifiers has been found to reduce signal distortion during transmissions, it can substantially increase the overall size and cost of the multiple-transmission systems in which it is implemented. Thus, from the above, it can be appreciated that designers of such multiple transmission systems are faced with the decision of designing a low-distortion system having a high cost—due to a large number of power amplifiers, or a high-distortion system having a low cost—due to a small number of power amplifiers.